Please check the list below ( document) as a reference. This document can help a bit, but is never the answer to all questions because Nintendo made a real big mess with all these codes. Please ask me when you are in doubt or sent me an e-mail with tips
document source:
REGION CODES: Gameboy , GB Color and GB Advance do not have regionlocks (a USA game plays on a Euro Gameboy)
A code on cartridges can be the difference between a Spanish Language game or a English Language game ( for example Pokemon games). Most DMG cartridges are English only (with very little text sometimes). Some DMG and many CGB and GBA Games are multilingual (especially with EUR-CODE) . Boxes and manuals are another story. They where made in many, many languages, combinations etc.
There are very few "Dutch only" made games. Only with the obvious child games like Barbie where many text is used in-game there are "Dutch Only" versions. Even when a game like Bob the Builder or a Looney Tunes Game has an HOL code (Holland = Netherlands) on the cartridge label , the game is multilingual ( you choose your language when you start to play). If the Manual of "Bob de Bouwer" (or "Looney Tunes") says HOL on the cover too, in this case there is only Dutch (Nederlands) in the manual. There are also examples and exceptions where HOL on the manual accompanied with the text "Mode'Emploi" or "Instruction Booklet" does not only has Dutch inside but also "Francais" and/or "English". FAH usually means there is Francais and Dutch inside but a 3th or 4th language can occur too. Most EUR manuals have at least English and/or Deutsch and at least 4 to 6 languages. There are NOE (Nintendo of Europe) manuals that have English too but in general it's German (Deutschsprachig). I have a SCN (Scandinavian ) manual ( Snow White for CGB) that I thought would be for the Nordics/Scandinavian (Sweden Norway Denmark) but "only" had "Francais"and "Nederlands" inside (!)
Please do your research or ask me when you are in doubt!
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Here's a (growing) list of Game Boy Games where Language and Regioncode is very important when buying one. If you know more games please let me know. The List:
Pokémon Blue, Red and Yellow, Gold, Silver and Crystal ; All made in different Lingual editions.
Pokémon Sapphire, Leafgreen, Fire Red , Emerald ; All made in different Lingual editions.
Zelda Link's Awakening for D.M.G. ( examples NOE for German, HOL or UKV for English)
let me know what games to add here